1. Field of the Invention
The present invention relates to a process of forming a color photographic image, more particularly to a process of forming a color photographic image using a novel yellow-forming coupler, and a photographic element containing such coupler.
2. Description of Prior Art
For the formation of a color photographic image by a subtractive color process, a step is utilized in which the silver halide grains in an exposed silver halide photographic emulsion layer are reduced by a developing agent, generally an aromatic primary amine compound, in particular an N,N-di-substituted p-phenylenediamine compound, and the oxidation product of the developing agent formed at the same time causes a coupling reaction with color-forming couplers to give cyan, magenta, and yellow images.
Each coupler used in the color developing process is a compound having a phenolic hydroxyl group, an anilinic amine group, or an active methylene group which yields, by oxidative coupling with the aromatic primary amine developing agent, a dye capable of absorbing light in a visible wave length region.
A yellow dye image absorbs a blue light component in a wave length region of from about 400 millimicrons to about 500 millimicrons. Known yellow-forming couplers include .beta.-ketoacetoacetic acid esters, .beta.-diketones, N,N-malondiamides, .alpha.-acylacetamides, etc.
Among these yellow-forming couplers, benzoylacetamide type compounds have been widely used as good yellow-forming couplers in the field of color photography. Almost all of these yellow-forming couplers are 4-equivalent couplers, that is, couplers which require 4 mols of exposed silver halide as an oxidizing agent for forming one mol of azomethine dye. However, the incorporation of a large amount of silver halide in a photosensitive emulsion layer is accompanied with disadvantages, i.e., light scattering in the emulsion layer increases to reduce the sharpness of the image formed and the thickness of the emulsion layer increases to reduce the processing rate of the photographic light sensitive material. Furthermore, such a type of yellow-forming coupler also has the fault that the formation of the dye by the coupler is not completed in a color development which requires a strong oxidizing agent in a subsequent processing step.
In order to improve those faults, it has been proposed to use a so-called 2-equivalent coupler, that is, a coupler which requires only two mols of exposed silver halide to form one mol of methine dye.
A 2-equivalent yellow coupler has the structure where one of the hydrogen atoms of the active methylene group is substituted for by a coupling off or splitting off group. As examples of such coupling off groups, a fluorine atom is described in U.S. Pat. No. 3,277,155; a substituted phenoxy group in U.S. Pat. No. 3,408,194; an acyloxyl group in U.S. Pat. No. 3,447,928; a sulfoxyl group in U.S. Pat. No. 3,415,652; and also the compound shown by the following formula ##STR3## in West German Patent Application (OLS) No. 2,057,941.
The couplers disclosed in the above U.S. Patents and in U.S. Pat. Nos. 3,265,506 and 3,253,924 also have groups analogous to R.sup.1 and R.sup.2 in the present invention, and serve to illustrate the wide class of groups which can serve as acceptable R.sup.1 and R.sup.2 groups in the present invention.
However, many of these known couplers have faults, i.e., they are insufficient in coupling reactivity, they give high color fog, the coupling activity of the couplers in photographic lightsensitive materials gradually reduces due to the instability of the couplers themselves, they cause stain, the yellow dyes formed from such couplers are weak in preservation stability, and/or they are not easily produced. In short, many of such couplers are not always satisfactory.